The invention relates in general to munitions and in particular to methods for safeguarding munitions that may be exposed to unplanned stimuli.
United States law may require that munitions meet certain safety standards, known as insensitive munition (IM) standards, to protect against unplanned stimuli. Two tests may be used to simulate munitions exposed to a fire, a slow cook off test (SCO) and a fast cook off test (FCO). In SCO, a munition in packaged configuration may be heated at a rate of 6° F./hour until the munition reacts. In FCO, a munition may be engulfed in a flame of at least 800° C. until the munition reacts. It may be desirable for the reaction to be limited to no more than burning (Type 5 reaction). A detonation (Type 1 reaction) may not be acceptable.
Munitions may demonstrate a Type 1 reaction when exposed to either the SCO or FCO tests. It has been found that when propellant is heated, gases may be given off and, if pressure is allowed to accumulate in a cartridge, the munition may detonate. Venting the gases may delay the point in time at which the detonation occurs. If the venting of gases is adequate, the propellant may burn vigorously without detonating.
Previous attempts at venting munitions have involved melt-away round plugs or threaded plugs. Some ionomer plastic plugs may not fully melt, thereby obstructing the vent. Some eutectic metal plugs may have a low tensile and shear strength, thereby causing the plug to fail under test firing. Some cartridges, for example, 25 mm cartridges, have been most difficult to render IM compliant. The difficulty may be due to the high propellant pressure generated and/or the small cartridge diameter.
Other munitions, such as grenades, for example, also generate gases when heated. A grenade, such as the M67 grenade, may contain a primary energetic material such as Composition B. If pressure is allowed to accumulate in the grenade body, the Composition B may detonate. If venting is adequate, the Composition B may burn vigorously without detonating. Past attempts at IM compliance included removing the fuse from the grenade to create a vent, or threading the circumference of the grenade body so that the grenade may split in half when the internal pressure rises. Neither solution has proven satisfactory.
A need exists for apparatus and methods for rendering munitions compliant with IM standards.